Cutoff mechanisms for repetitively cutting a moving web into sheets of selectively variable lengths operate within a predetermined range. In the corrugated paperboard industry, most of the cutoff mechanisms used heretofore have had a range of about 200 inches for sheet length, with the maximum size sheet being 240 inches long.
The industry has always had a desire for a cutoff mechanism which could cut sheets within the normal range but could also cut sheets having a length much greater than that available. Recently, there has been a demand for a cutoff machine capable of selectively and accurately cutting a moving web into sheet lengths varying from about 24 inches to about 480 inches.
U.S. Pat. No. 3,745,865 discloses a cutoff mechanism having a variable cyclic mechanism so that a moving web may be cut into sheets having lengths from about 22 inches up to about 240 inches. U.S. Pat. No. 3,628,410 discloses a device for extending the sheet length beyond 240 inches by providing a web length counter and a stop-start mechanism whereby the cutoff is inoperative for a period of time during which a predetermined length of the web is advanced.
The present invention is directed to apparatus for repetitively cutting a moving web into sheets by means of a cutting blade movable in the direction of travel of the web at the speed of the web at the instant of cutting. The cutting blade is mounted on a rotatable support and driven by a cyclic mechanism selectively adjustable for the length of sheets to be cut from the web. The cyclic mechanism is driven by a main drive shaft. A driving motor is connected to the main drive shaft through a variable speed drive.
The present invention preferably includes a selectively operable transmission whereby the main drive shaft may be driven at a uniform speed or at a cyclic speed. When the drive shaft is driven at a cyclic speed the period of the cutting blade is extended so that the interval between cuts is longer. A longer period permits a greater length of web to pass through the apparatus between cuts and a proportionately longer sheet may be cut without an interruption in the motion of the blade. The addition of the present invention to conventional cut-off machines doubles the maximum length sheet which may be repetitively cut from a continuously moving web.
One aspect of the present invention is the advantage, in some circumstances, of being able to rapidly change from one sheet length to another. With a conventional machine having a uniform speed input to the cyclic mechanism, it could take as long as 30 seconds to change from a sheet length of 40 inches to a sheet length of 100 inches. With the present invention, it is only necessary to change from a sheet length of 40 inches to a sheet length of 50 inches and then flip a switch so that a cyclic input is transmitted to the cyclic mechanism to attain a sheet length of 100 inches.
It is an object of the present invention to provide a cutoff mechanism selectively operable in either of two modes with the second mode providing for a sheet length up to twice the sheet length attainable by the first mode.
It is another object of the present invention to provide a device which facilitates increasing maximum sheet length from about 240 inches to about 480 inches and which is adaptable for incorporation in new machines or for converting old machines.
It is another object of the present invention to reduce conversion time when changing from a set-up for one sheet length to a set-up for another sheet length.
Other objects and advantages will be set forth hereinafter.